JP5833327B2 - X-ray tube and X-ray analyzer - Google Patents

Description

  The present invention relates to an X-ray tube including a cathode and an anode and housed in a cylindrical envelope, and an X-ray analyzer including the X-ray tube.

  The X-ray fluorescence analyzer can specify the constituent elements of the sample and the concentration thereof. The sample is irradiated with primary X-rays generated by an X-ray tube. Thereby, fluorescent X-rays peculiar to the elements contained in the sample are emitted from the sample. It is possible to identify elements by detecting fluorescent X-rays and analyzing energy, and to measure the concentration and the like based on the number of elements.

  Focusing on the measurement time, the measurement time can be shortened by increasing the primary X-ray intensity and the secondary X-ray detection efficiency. For example, an X-ray tube characterized by increasing the primary X-ray intensity is disclosed (see Patent Document 1). The disclosed x-ray tube includes a conical axial end that supports a window, an anode disposed adjacent to the anode pipe, and an electro-optic device. The primary X-ray intensity is increased by reducing the distance between the anode serving as the X-ray generation source and the sample. On the other hand, the radius of the light source is about 0.5 mm, which is very large compared to a side window type or transmission type X-ray tube. Collimators and X-ray conduits are used to limit the irradiation area. When the light source radius is about 0.5 mm, the optimal analysis area size is about 1 mm (see Patent Document 2).

JP-T-2001-504988 JP-A-5-275035

  In order to analyze a small area of a sample in a short time, it is necessary to irradiate the analysis area with a primary X-ray having a high intensity.

  However, when the analysis region is on the order of several hundred μm, the angular spread of the irradiated X-rays is large at a light source radius of about 0.5 mm, so it is necessary to use a collimator having a diameter smaller than the irradiated radius. On the other hand, the intensity of the irradiated X-ray depends on the diameter of the collimator. Accordingly, when a collimator having a small diameter is used, the irradiation X-ray intensity is reduced even with a large light source.

  The present invention has been made in consideration of such circumstances, and an object of the present invention is to provide an X-ray tube capable of emitting high-intensity X-rays even in a small analysis region.

In order to achieve the above object, the present invention provides the following means.
An X-ray tube according to the present invention includes an anode target that emits X-rays by collision of an electron beam, a plurality of cathode electrodes that are disposed at a position facing the anode target, and that emits an electron beam, and an irradiation direction of the electron beam. An electron optical system to be controlled; an envelope that accommodates the anode target, the cathode electrode, and the electron optical system; and a hemispherical electrode that is provided on an inner wall of the envelope so as to surround the anode target . Thereby, the irradiation amount of the electron beam to the anode target can be increased. Thereby, an electric field for irradiating the electron beam toward the anode target can be formed between the cathode electrode and the anode target. Therefore, the electron beam is intensively applied to the anode target.

  In addition, the electron optical system of the X-ray tube according to the present invention controls the irradiation direction of the electron beam to be substantially perpendicular to the surface of the hemispherical electrode. Thereby, the electron beams emitted from the plurality of cathode electrodes can be intensively irradiated toward the anode target.

  Further, the anode target of the X-ray tube according to the present invention has a recess in the direction of emitting the X-ray. As a result, an electric field for concentrating the electron beam in the concave portion can be formed around the anode target. Therefore, the electron beam irradiation can be concentrated on the concave portion.

  Moreover, the X-ray tube which concerns on this invention has the protrusion part which protruded toward the anode target in the inner wall of an envelope. As a result, an electric field for concentrating the electron beam in a small area on the anode target can be formed inside the envelope. Moreover, it is preferable to arrange | position a protrusion part near the edge part of a hemispherical electrode. This can create a stronger electric field that concentrates the electron beam in a small area on the anode target.

  In addition, the cathode electrode of the X-ray tube according to the present invention is installed in a groove provided in a part of the envelope. Thereby, a some cathode electrode can be installed in the hemispherical electrode side. Therefore, a large amount of electron beam can be irradiated to the anode target.

  Further, the electron optical system of the X-ray tube according to the present invention includes an extraction electrode having a surface substantially parallel to the hemispherical electrode. Thereby, the electron beam emitted from the cathode electrode can be irradiated toward the anode target.

  An X-ray analyzer according to the present invention detects the X-ray tube, the sample stage on which the sample is placed, a collimator for limiting the amount of X-ray irradiation to the sample, and the fluorescent X-rays emitted from the sample And a detector. Thereby, high intensity | strength X-rays can be irradiated to a small analysis area | region. In addition, the spread angle of the X-rays that have passed through the collimator can be reduced. Therefore, for example, even when analyzing with a long working distance in order to analyze a sample with large irregularities, high intensity X-rays can be irradiated to a small analysis region.

  The X-ray tube according to the present invention can irradiate a small analysis region with high-intensity X-rays. Thereby, analysis time can be shortened.

It is a lineblock diagram of the X-ray tube concerning the embodiment of the present invention. It is a figure which shows the result of the electric field simulation of the X-ray tube which concerns on embodiment of this invention. It is a distribution map of the electron which collides with the anode target which concerns on embodiment of this invention. 1 is a configuration diagram of an X-ray analysis apparatus according to an embodiment of the present invention. FIG. 4 is a relationship diagram between a radius of an X-ray light source and an X-ray intensity ratio according to an embodiment of the present invention. It is a lineblock diagram of the X-ray tube concerning the embodiment of the present invention.

  Hereinafter, embodiments of the X-ray tube according to the present invention will be described. FIG. 1 is a configuration diagram of an X-ray tube. The X-ray tube has a shape in which a cylindrical shape and a hemispherical shape are connected. The cathode filament 1 emits an electron beam 2. The electron beam 2 is applied to the anode target 4 connected to the anode electrode 3. The anode target 4 emits X-rays 5 by irradiation with the electron beam 2. The X-ray 5 is emitted out of the X-ray tube from the window 6 provided in a part of the envelope 14 facing the anode electrode 3. The window 6 is a beryllium plate having a thickness of 125 μm, for example.

  The envelope 14 is disposed so as to cover the anode target 4. In particular, the envelope 14 has a hemispherical shape, and the anode target 4 is preferably disposed near the center thereof. The cathode filament 1 is installed in a plurality of grooves 8 provided in the envelope 14. Thereby, a plurality of cathode filaments 1 can be installed toward the anode target 4. Then, by installing the cathode filament 1 in the hemispherical envelope 14, the electron beam 2 can be concentratedly irradiated on the anode target 4 at the center of the hemispherical shape. Therefore, the anode target 4 can be irradiated with a plurality of large amounts of electron beams 2.

  The envelope 14 is connected to the envelope 15 on the anode electrode 3 side. The inside of the X-ray tube is in a vacuum state. Inner wall electrodes 9 and 10 are provided on the inner walls of the envelopes 14 and 15, respectively. The inner wall electrodes 9 and 10 are grounded.

  An extraction electrode 11 is installed as an electron optical system between the cathode filament 1 and the anode target 4. The extraction electrode 11 has a surface parallel to the curved surface of the inner wall electrode 9 of the envelope 14. That is, the extraction electrode 11 has a spherical surface.

  The cathode filament 1 is connected to a current source 16. The cathode filament 1 is energized and heated, and electrons are emitted from the cathode filament 1. The emitted electrons are extracted by a positively applied extraction electrode 11 to form an electron beam 2. A high voltage is applied to the anode electrode 3 by the voltage source 17. Thereby, the electron beam 2 is irradiated toward the positively applied anode target 4.

  The electron beam 2 is irradiated substantially perpendicularly to the surface of the extraction electrode 11. That is, the electron beam 2 is irradiated substantially perpendicularly to the surface of the extraction electrode 11 having a surface substantially parallel to the hemispherical inner wall electrode 9 disposed so as to cover the anode target 4. Therefore, the electrons emitted from the cathode filament 1 can be irradiated toward the anode target 4.

  The anode target 4 has a recess 12 on the side from which the X-ray 5 is emitted. Thereby, an electric field that allows the electron beam 2 to collect in the recess 12 can be formed around the anode target 4. Therefore, the electron beam 2 can be concentrated in the recess 12.

  The envelope 15 has a protrusion 13 that protrudes toward the anode target 4. As a result, an electric field in which the electron beam 2 is collected on the anode target 4 can be formed. Therefore, the electron beam 2 can be concentrated on the anode target 4.

  FIG. 2 is a diagram showing the result of electric field simulation of the X-ray tube according to the embodiment of the present invention. The set dimensions of the simulation are as follows. The distance between the window 6 side of the inner wall electrode 9 and the anode target 4 is 5 mm. The diameter of the inner wall electrode 10 of the envelope 15 is 8.2 mm. The diameter of the anode electrode 3 is 3 mm. The height of the protruding portion of the recess 12 of the anode target 4 is 1 mm. The diameter of the bottom portion of the recess 12 is 1.2 mm. Here, a conical shape is used for the protruding portion of the recess. The height of the protrusion 13, that is, the length in the normal direction of the X-ray tube is 0.7 mm. The width of the protrusion 13, that is, the length in the longitudinal direction of the X-ray tube is 1 mm.

  The electric field formed when a voltage is applied with the above set dimensions is indicated by an equipotential line 21. Due to the shape of the inner wall electrode 9 and the extraction electrode 11, the electric field in the vicinity of the inner wall electrode 9 and the extraction electrode 11 forms a hemispherical electric field centering on the anode target 4.

  Further, an electric field acting on the electron beam 2 is formed between the protruding portion 13 and the extraction electrode 11 so as to go to the anode target 4 due to the shape of the protruding portion 13. Thereby, the electron beam 2 can be concentratedly irradiated to the anode target 4. Here, in order to form an ideal electric field, it is desirable that the projecting portion 13 be installed near the end of the inner wall electrode 9, that is, near the connecting portion between the inner wall electrode 9 and the inner wall electrode 10. On the other hand, when there is no protrusion 13, the electric field in the vicinity of the inner wall electrode 10 from the extraction electrode 11 becomes an electric field that acts on the electron beam 2 so that the electron beam 2 is irradiated to the anode electrode 3 side of the anode target 4. The electron beam 2 cannot be concentrated on the anode target 4.

  Furthermore, the recess 12 of the anode target 4 reinforces the concentration effect of the electron beam 2. The electron beam 2 is irradiated toward the center of the hemisphere by the electric field formed by the inner wall electrode 9 and the extraction electrode 11. However, since the anode target 4 has a finite size, the electric field generated by the anode target 4 and the inner wall electrode 9 weakens the focusing effect of the electron beam 2. Therefore, the recess 12 is provided in the anode target 4. As a result, an electric field in which the electron beam 2 is concentrated on the bottom portion of the recess 12 is formed around the anode target 4. Therefore, the electron beam 2 can be focused on a small area on the anode target 4.

  FIG. 3 is a distribution diagram of electrons 31 that have been irradiated with the electron beam 2 by an X-ray tube subjected to electric field simulation and collided with the anode target 4. By using the X-ray tube of the embodiment of the present invention, it is possible to irradiate the electron beam 2 intensively to a small area of the anode target 4 having a radius of 0.2 mm.

  FIG. 4 is a configuration diagram of an X-ray analyzer equipped with the X-ray tube according to the embodiment of the present invention. The X-ray irradiation unit 41 equipped with the X-ray tube of the embodiment of the present invention irradiates X-rays 43. The irradiation amount and irradiation area of the X-ray 43 are limited by the collimator 42. The X-ray 43 is applied to the sample 45 placed on the sample table 44. Thereby, the fluorescent X-ray 46 is emitted from the sample 45. The fluorescent X-ray 46 is detected by the detection unit 47. The detection unit 47 outputs a detection signal to the processing unit 48. The processing unit 48 processes the input detection signal and causes the display unit 49 to display the detection result.

  FIG. 5 is a relationship diagram between the radius of the X-ray light source and the X-ray intensity ratio. The relationship diagram is the result of simulation. The distance between the X-ray light source of the X-ray irradiation unit 41 and the collimator 42 is 50 mm, and the distance between the collimator 42 and the sample 45 is 10 mm. The X-ray intensity ratio was based on the X-ray intensity when the radius of the X-ray light source was 0.5 mm. The irradiation beam diameter is an area for calculating the X-ray intensity. This is a spread of the X-ray 43 which is limited by the collimator 42 and is irradiated on the sample 45.

  When the radius of the X-ray light source is reduced, the X-ray intensity increases. In particular, when the irradiation beam diameter is 0.2 mm, the X-ray intensity greatly increases when the radius of the X-ray light source is reduced. That is, in the case of the irradiation beam diameter of 0.5 mm limited by the large-diameter collimator 42, the X-ray intensity increased by reducing the X-ray intensity radius is small. This means that since the diameter of the collimator 42 is large, the amount of X-rays reaching the sample 45 does not change greatly even if the radius of the line light source is changed. On the other hand, in the case of the irradiation beam diameter of 0.2 mm limited by the small-diameter collimator 42, the X-ray intensity increased by decreasing the X-ray intensity radius is large. This is because, since the diameter of the collimator 42 is small, the amount of X-rays reaching the sample 45 is reduced when the radius of the X-ray light source is large. Therefore, in order to irradiate a small area of the sample 45 with high-intensity X-rays using the collimator 42 having a small diameter, it is necessary to use an X-ray light source having a small radius.

  According to the X-ray analyzer equipped with the X-ray tube of the embodiment of the present invention, even when the irradiation beam diameter is reduced, the X-ray light source has a small radius, so that the sample can be irradiated with high-intensity X-rays. . Therefore, the measurement time of the sample can be shortened.

  Another embodiment of the X-ray tube according to the present invention uses a field emission type electron source instead of the cathode filament 1. FIG. 6 shows an X-ray tube using a carbon nanotube array 61 as a field emission type electron source. The carbon nanotube array 61 is an array in which carbon nanotubes are oriented toward the anode target 4. Even if the extraction electrode 11 is not installed, the carbon nanotube can be irradiated with the electron beam 2 in the oriented direction. Accordingly, the carbon nanotube array 61 can be installed on the inner wall of the envelope 14 without providing the groove portion 8. Therefore, a plurality of carbon nanotube arrays 61 can be installed on the inner wall of the envelope 14 and the anode target 4 can be irradiated with a large amount of electron beam 2. Further, since the carbon nanotube array 61 can irradiate the electron beam 2 from the tip of the carbon nanotube, it is an electron source having a high emission electron density. Therefore, a large amount of the electron beam 2 can be irradiated to the anode target 4.

  According to the X-ray analyzer equipped with another X-ray tube according to the embodiment of the present invention, a large amount of electron beams can be intensively irradiated onto the anode target, so that the sample is irradiated with high-intensity X-rays. be able to.

DESCRIPTION OF SYMBOLS 1 ... Cathode filament 2 ... Electron beam 3 ... Anode electrode 4 ... Anode target 5 ... X-ray 6 ... Window 8 ... Groove part 9, 10 ... Inner wall electrode 11 ... Extraction electrode 12 ... Recessed part 13 ... Projection part 14, 15 ... Envelope DESCRIPTION OF SYMBOLS 16 ... Current source 17 ... Voltage source 21 ... Equipotential line 31 ... Colliding electron 41 ... X-ray irradiation part 42 ... Collimator 43 ... X-ray 44 ... Sample stand 45 ... Sample 46 ... Fluorescent X-ray 47 ... Detection part 48 ... Processing Part 49 ... Display part 61 ... Carbon nanotube array

Claims (9)

An anode target that emits X-rays by electron beam collision;
A plurality of cathode electrodes disposed at positions facing the anode target and emitting the electron beam;
An electron optical system for controlling the irradiation direction of the electron beam;
An envelope containing the anode target, the cathode electrode, and the electron optical system;
A hemispherical electrode provided on the inner wall of the envelope so as to surround the anode target;
X-ray tube having   The X-ray tube according to claim 1, wherein the electron optical system controls the irradiation direction of the electron beam to be substantially perpendicular to a surface of the hemispherical electrode.   The X-ray tube according to claim 1, wherein the electron optical system includes an extraction electrode having a surface substantially parallel to the hemispherical electrode.   The X-ray tube according to claim 1, wherein the anode target has a recess in a direction in which the X-ray is emitted.   The X-ray tube according to any one of claims 1 to 4, further comprising: a protruding portion protruding toward the anode target on an inner wall of the envelope.   The X-ray tube according to claim 5, wherein the protrusion is disposed at an end of the hemispherical electrode.   The X-ray tube according to claim 1, wherein the cathode electrode is installed in a groove provided in a part of the envelope. An anode target that emits X-rays by electron beam collision;
A cathode electrode comprising a plurality of carbon nanotubes disposed at a position facing the anode target and emitting the electron beam;
An envelope containing the anode target and provided with the cathode electrode;
The envelope includes a closed hemispherical portion and a cylindrical portion surrounding the anode target, and the cathode electrode constitutes an inner wall electrode attached along the inner wall of the hemispherical portion , and the carbon nanotube is An X-ray tube arranged to be oriented toward the anode target. X-ray tube according to any one of claims 1 to 8,
A sample stage on which the sample is placed;
A collimator for limiting the amount of X-ray irradiation to the sample;
A detector for detecting fluorescent X-rays emitted from the sample.

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